1. Field of the Invention
The present invention relates to an improved shaft seal. More specifically, the present invention relates to a shroud for a face seal having a resilient bellow or diaphragm urging a rotating seal component axially of a shaft against a stationary seal component, particularly in a centrifugal pump adapted for pumping liquid or slurries containing particulates.
2. Prior Art
A representative shaft seal used in connection with a centrifugal pump is shown in Rockwood et al. U.S. Pat. No. 4,406,465, issued Sept. 27, 1983. In such an application, it has been found to be desirable to use a "face seal" which has a stationary component with a flat, precisely machined, radial surface and a rotating component having an abutting flat radial surface similarly precisely machined. A resilient member biases the rotating component against the stationary component.
To assure a reliable leak-proof seal in a variety of applications, the construction of face seals has become increasingly complex, as illustrated by the seal constructions shown in Van Vleet U.S. Pat. No. 3,188,095, issued June 8, 1965; Van Vleet U.S. Pat. No. 3,184,244, issued May 18, 1965; Azibert U.S. Pat. No. 4,576,384, issued Mar. 18, 1986; and Azibert et al. U.S. Pat. No. 4,625,977, issued Dec. 2, 1986.
An economical alternative is a "welded metal bellows seal" which has a set of stacked rings acting similarly to a Belleville spring but with edges of adjacent rings welded together. The stack of rings form the resilient member for biasing the rotating seal component axially of the shaft against the stationary seal component. The "Type 680" seal available from EG&G SEALOL of Cranston, R.I., is representative of the bellows seal. Such seal works quite well in some centrifugal pump applications. In some applications, however, the liquid or slurry to be pumped contains abrasive particulates. Vaughan U.S. Pat. No. 3,774,323, issued Nov. 27, 1973, for example, shows a centrifugal pump used for dredging. The dredged material may contain grit such as sand. Similarly, Vaughan U.S. Pat. No. 3,973,866, issued Aug. 10, 1976, discloses a pump for slurries containing solids which may include abrasive particulates. For such applications, the gritty or abrasive material can cause premature deterioration of the exposed welds of the resilient bellows, destroying the integrity of the economical welded metal bellows seal.